A. C. Rodrigues

Technical note: Relationship between infrared thermography and heat production in young bulls

The traditional techniques to measure heat production (HP) are calorimetry (direct and indirect) and comparative slaughter. Both methods are expensive and require extensive amounts of time and infrastructure. Infrared thermography (IRT) could be a faster and less expensive alternative to estimate cattle HP. The objective of this project was to evaluate the use of the IRT technique as an indicator of HP in cattle. A total of 24 bulls (12 Nellore and 12 Black Angus) with initial BW of 380 ± 7 kg were used. Initially, 4 animals of each breed were harvested (baseline animals) and simple regressions were developed for each breed from these baseline animals to estimate the initial chemical composition of the remaining bulls. Eight animals of each breed were fed a silage/concentrate diet for ad libitum intake in individual stalls. On the 25th, 50th, and 75th experimental day, infrared thermal images (Fluke Ti 55ft; Fluke Corporation) were taken of each animals face to access skin and ocular surface temperatures. A metabolism trial was conducted to estimate the ME intake (MEI). After 84 experimental days, the cattle were harvested and retained energy (RE) and HP were calculated. The data were analyzed using the MIXED and REG procedures of SAS adopting a significance level of 0.05. Angus cattle had a greater daily MEI, HP, and skin and eye temperatures than Nellore. We found significant correlations ( ≤ 0.005) between daily HP and maximum ( = 0.65) and average skin temperatures ( = 0.65) and maximum ( = 0.65) and average ocular surface ( = 0.69) temperatures recorded on d 50. Infrared thermography has potential to be used to evaluate HP in cattle.

Expression of genes related to the regulation of muscle protein turnover in Angus and Nellore bulls.

We aimed to evaluate the expression of genes related to the regulation of muscle protein turnover in the longissimus dorsi (LD) muscle of Angus and Nellore bulls and to estimate the within-breed correlations of gene expression and performance traits. Thirteen genes related to the IGF-1 and myostatin pathways were studied. Thirteen animals, with an initial average BW of 381.2 ± 11.8 kg, from each breed were used in a completely randomized 2 × 2 factorial design (2 breeds and 2 feeding levels). The diet consisted of corn silage and a corn-soybean meal concentrate in a roughage-to-concentrate ratio of 30:70. Cattle were fed ad libitum (with 9 animals from each breed) or feed restricted (a 55% restriction of total DMI of ad libitum-fed animals, calculated as percentage of metabolic BW, with 4 animals of each breed). The experimental period lasted for 82 d and it was preceded by a 28-d adaptation period. The performance traits evaluated were slaughter body weight, total ADG (from d 1 to 82 of the trial), initial ADG (from d 1 to 41 of the trial), final ADG (from d 42 to 82 of the trial), total DMI (from d 1 to 82 of the trial), initial DMI (from d 1 to 41 of the trial), final DMI (from d 42 to 82 of the trial), HCW, LD weight (LDW), and rib eye area (REA). After slaughter, samples were taken from the LD muscle between the 12th and 13th ribs for gene expression analysis by quantitative reverse transcription PCR. There was no difference ( > 0.05) in the expression of any of the genes studied between ad libitum-fed Angus and ad libitum-fed Nellore, whereas feed restriction increased the expression of (; < 0.001), (; = 0.05), and (; = 0.04) and decreased the expression of ( < 0.01). The REA was negatively correlated to (; = 0.01), (; = 0.02), and ( = 0.05). The HCW was negatively correlated to ( = 0.01) and ( = 0.01) and tended to be negatively correlated to ( = 0.07), whereas the LDW tended to be negatively correlated to ( = 0.08). The genes , , and seem to be important for muscle growth and may be worthy of further investigation as future strategies for increasing muscle in livestock.

Effect of heat stress on intake and metabolism of Bos taurus (Angus) and Bos indicus (Nellore)

During heat stress, ruminants like other homeothermic animals, use pathways to increase heat loss and reduce heat production to maintain euthermia (Bernabucci et al., 2010). Environmentally induced hyperthermia decreases efficiency and production (O’Brien et al., 2010). One of the first noticeable signs of heat stress (HS) during production is reduced nutrient intake, which is presumably an evolutionary strategy to reduce the ‘heat increment’ of feeding (O’Brien et al., 2010). The aim of this study was to evaluate the effect of different air temperatures on diurnal, nocturnal, and daily feed intake as well as water intake, heart rate, respiratory rate and body temperature.